Why is the pseudo element smaller than the parent?

Question

css

Good afternoon. Can you please tell me why the pseudo-element is smaller than the parent?
Above is a span and below is a pseudo element Span

Styles:
.header__burger-btn span {
width: 100%;
height: 1px;
border: 2px solid #202020;
position: absolute;
}
Pseudo element style:
.header__burger-btn span::before {
content: "";
position: absolute;
width: 100%
height: 100%;
top: 10px;
border: 2px solid #202020;
}

Answer 1

because in width width: 100%; the pseudo-element does not have a parent border

Answer 2

The pseudo-element is inside the parent. And occupies 100% of its internal width .